Endoscopy systems, consisting of an endoscope and a light source, are used for endoscopy in medical or non-medical applications—in the latter case also known as boroscopy. The light source can be integrated in the endoscope, in particular in its distal end, or can be present as a separate unit, which is optically coupled with an endoscope by a light conductor cable. Light from the light source emerges at the distal end of the endoscope and there illuminates an object to be investigated. Light remitted by the object is captured by a lens on the distal end of the endoscope and conducted onto a light-sensitive image sensor or conveyed, for example by means of an oriented bundle of lightwave conductors or a rod lens system, to the proximal end of the endoscope. In the latter case the light remitted by the object can be observed on the proximal end of the endoscope by an eyepiece or is recorded by means of a video camera. As an alternative or in addition to remitted light, light emitted by the object can also be observed, in particular fluorescent light.
The quality of an image recorded by an endoscopy system, in particular brightness, brightness-color contrast, signal-noise ratio, color fidelity and resolution or sharpness, depends on the observed object, in particular its optical properties, and above all on the endoscopy system. Relevant factors are, for example, the functionality of the light source, its radiant capacity or the light beam generated by it, the spectrum of generated light, in some cases the transmission properties of an employed light conductor cable and the coupling of the light conductor cable with the light source and with the endoscope, the functionality of the light transmission within the endoscope, the degree of effectiveness of the uncoupling of light from the light source out of the endoscope, the functionality or optical properties of the observation beam path in the endoscope, possibly including an oriented bundle of lightwave conductors or a rod lens system, the functionality of the eyepiece or video camera. Frequent sources of failure are, among others, the light source subjected to an alteration process, possibly the light conductor cable and its coupling to the light source and the endoscope, and the coupling of a video camera to the endoscope.
Fluorescent light is observed for medical-diagnostic purposes in particular. In photodynamic diagnostics (PDD), for example, a fluorescence of protoporphyrin IX induced by administered 5-aminolevulinic acid (ALA) is observed. Enrichment of ALA and thus also the intensity of the fluorescence depend on the condition of the tissue. In autofluorescence diagnostics (AF diagnostics) the fluorescence of bodily-produced fluorophores is observed, whose concentration is likewise dependent on the condition of the tissue. Fluorescent diagnostic methods are used in fields other than medicine as well.
To prevent remitted excitation light or illuminating light from outshining the fluorescence, an illumination filter is used in the illumination or excitation beam path between light source and object and in the observation beam path between object and video camera or eyepiece. The illumination filter is a short pass filter, which essentially transmits only the short wavelengths required to excite the fluorescence, but on the other hand primarily or almost exclusively reflects or absorbs longer wavelengths. A very reduced, but not disappearing, transmission in the blocking range is desired with many applications in order to receive, even without fluorescence, an image that has a low brightness but is visible. The observation filter is a long pass filter that transmits only wavelengths of fluorescence and reflects or absorbs short-wave illuminating light remitted by the object. Illumination or excitation filters can as a rule be manually or mechanically exchanged or changed. Observation filters can be replaceable or changeable, but in many cases are firmly built into the endoscope. In urology, for example, for observation in white light, ALA or AF fluorescence, various endoscopes are used that, at least in the observation beam path, are optimized for their respective use or have a corresponding filter characteristic. The aforementioned sources of failure or influences on functionality of the endoscopy system include, in the case of observation of fluorescence, the combination of the illumination filter or spectrum of the light source on the one hand and of the observation filter on the other hand.
A corresponding problem exists with other optical investigation systems, which include an imaging device, a light source and a video camera for optical investigation of medical and non-medical objects in remitted light and/or in fluorescent light. These include exoscopes, which for instance are used for diagnostics and for microsurgical procedures on or close to bodily surfaces.
DE 196 38 809 A1 describes a device for testing and/or adjusting a PDD or PDT (photodynamic therapy) system and/or for training on a system of this type. Positioned in a housing is a target, opposite to which a distal end of an endoscope can be mounted. The curvature of the target can correspond to the variable field curvature of an imaging unit of the endoscope. A photo element and light sources are provided in the target. The photo element records the illuminating strength of an excitation light emitted from the endoscope. A control unit guides the light sources as a function of the illuminating strength recorded by the photo element.
DE 198 55 853 A1 describes an apparatus for testing and/or adjusting a PDD or PDT system and/or for training on a system of this type. The apparatus includes a luminescent phantom with a fluorescent dye. One end of an endoscope can be positioned opposite the luminescent phantom.
In the post-published DE 10 2009 043 696, an apparatus and a method for testing endoscopes are described. The apparatus includes a filter module with several perforations in which optic filters are positioned. The filter module is illuminated from one direction by the light source via a light conductor cable. From an opposite direction the light transmitted by the filter module is observed by means of an endoscope.
Each of the apparatuses and methods known by now, depending on concrete task assignments arising in practice, have advantages and disadvantages. For example, under some conditions and for a few applications none of the described apparatuses and methods allows a reliable testing of a complete endoscopy system or of a different complete optical investigation system in precisely the condition in which it was used or is used medically or non-medically before or afterward.
A disadvantage of the apparatuses and methods described in DE 196 38 809 A1 and in DE 198 55 853 A1 consists in the fact that the video camera automatically post-controls a minor erroneous image brightness, so that it is partially or completely compensated by the camera system and only at very reduced lighting does the image become recognizably poor. Something similar occurs with the human eye. In particular in fluorescent diagnostics, however, the risk of an incorrect diagnosis, in particular the overlooking of a tumor, exists immediately beforehand.